The present invention relates to an arrangement for hydraulically conveying solids in form of a slurry in general, and more particularly to a three-chamber hydraulic conveying arrangement.
There are already known various arrangements of the type here under consideration, particularly for use in hydraulically conveying coal, ore and similar particulate material over substantial elevational differences such as, for instance, 1,000 meters and/or large distances. One of such conventional arrangements includes a three-chamber conveying arrangement which is filled and discharged in countercurrent and in which valves are provided at the spaced ends of the chambers.
The prior art has been faced with the problem of conveying particulate material over large distances and/or over substantial elevational differences, and several solutions to such a problem have already been proposed. One of the most economical and efficient arrangements for conveying particulate material in form of a slurry involves a pressurizable chamber which can be operated on the principle of a lock or a sluice. To be more precise, the chamber is filled with a slurry at nominal superatmospheric pressure so that conventional slurry pumps which are capable of pumping slurry in substantial quantities but with only a small pressure head, can be used for this purpose. On the other hand, once the chamber is filled with slurry, further filling with slurry is terminated and pressurized hydraulic fluid, such as water, is admitted into the chamber and discharges the slurry therefrom into a discharge conduit through which the slurry is conveyed to another location of use or for treatment. Inasmuch as the medium which propels the slurry into the discharge conduit is clear water, that is water which does not contain any substantial amount of particulate material entrained therein, high-output pumps, such as centrifugal pumps, which are capable of generating substantial velocity and pressure heads, but which are sensitive to the influence of particulate material entrained in the fluid being pumped, can be used for discharging the slurry from the chamber into the discharge conduit. Such high-output pumps are very efficient, and also economical to operate.
It will be appreciated that, if only one such chamber were used, the flow of the slurry in the discharge conduit would be intermittent, which will be very disadvantageous, particularly since the material entrained in the fluid column in the discharge conduit would settle during the period of interruption and thus clog the discharge conduit. Therefore, it has already been proposed to utilize two or three chambers in an arrangement for hydraulically conveying solids, which chambers are similarly configurated and arranged and operated all in the same way. The chambers are generally elongated and provided with valves at their ends, which valves control the filling and the emptying of the respective chambers. Furthermore, it is also already known to provide pressure equalization valves at the ends of the chambers, such pressure equalization valves serving the purpose of bringing, without water hammer effect, the filled chamber to the pressure delivered by the high-output pump, and the chamber which is emptied from the slurry to the atmospheric pressure preparatory to filling of the chamber with a further charge of slurry. The pressure in the chambers is measured by means of conventional pressure-measuring devices. The conventional arrangements of this type further include a slurry pump as well as a pump for the pressurized hydraulic fluid, with their associated control devices which are capable of varying the filling and the discharging speed, and a specific weight measuring device for monitoring the concentration of the slurry.
The multi-chamber arrangements operate in accordance with the lock principle which has been discussed above, that is, each of the chambers is filled with the slurry delivered by the slurry pump at only slightly above the atmospheric pressure, and is emptied at a pressure delivered by the pump for the pressurized hydraulic fluid. This multi-chamber arrangement avoids the formation of sedimentation beds in the discharge conduit, and thus clogging of the discharge conduit, in that such an arrangement is capable of maintaining steady flow of the slurry through the discharge conduit.
The arrangements of this type are operated either in the concurrent, or in the countercurrent manner. In the first case, both the low pressure slurry and the high pressure hydraulic fluid are admitted at the same end of the chamber, and the pressurized slurry is discharged from the chamber into the discharge conduit at the other end of the chamber. In a countercurrent arrangement, the low-pressure slurry is admitted into the respective chamber at one end thereof, and discharged therefrom at the same end, the pressurized hydraulic fluid being admitted into the chamber at the other end thereof. The latter arrangement is more advantageous, particularly inasmuch as the chamber is completely emptied of slurry using the same amount of water, in that the larger and, consequently, heavier particles, which heavier particles have a higher degree of slippage relative to the carrier fluid than lighter particles, accumulate in the region of entry into the chamber, so that such heavier particles have to traverse a smaller distance to be discharged from the chamber than light particles.
Such hydraulic conveying arrangements are not usually built for continuous filling operations. In other words, the conventional arrangements, while assuring continuous flow in the discharge conduit, do not assure continuous flow of discharging slurry and do not assume continuous flow in the supply conduit of the low-pressure slurry. This is particularly true in view of the fact that relatively long time periods are needed for equalizing the pressure in the chambers, that is bringing the pressure in a full chamber to that of the pressurized hydraulic medium, or reducing the pressure of an empty chamber to substantially the atmospheric pressure. During such time periods, the filling operation must be interrupted inasmuch as the chambers can be filled only at about the atmospheric pressure. In order to assure the continuity of flow of the pressurized fluid through the discharge conduit, additional amounts of clear pressurized hydraulic fluid are forced through the discharge conduit. This means that not only is the efficiency of the arrangement reduced, but also additional amounts of the hydraulic fluid must be available. Also, the filling operation requires a longer period of time than the discharging operation so that, even if the pressurized hydraulic fluid is directly admitted into the discharge conduit during a period of pressure equalization, so that the additional pressurized hydraulic fluid need not flow through the empty chamber so that the pressure therein can be reduced simultaneously with increasing the pressure in the full chamber, the substantial difference between the filling and emptying time periods still necessitates availability of substantial amounts of additional pressurized hydraulic medium.
One of the most important disadvantages of the conventional hydraulic conveying arrangements is to be seen in the fact that the conveying capacity of the arrangement is rather low, especially in view of the fact that the slurry is unnecessarily diluted by the additional amounts of pressurized hydraulic fluid which need be introduced into the system during the pressure-equalization operation.
The conventional hydraulic conveying arrangements have chambers, preferably of tubular configuration, which are approximately 200 to 600 meters long. Thus, it will be appreciated that the filling and discharging times of such chambers are substantial, and so is the difference between the time needed for filling the chamber and the time required for emptying the chamber. Therefore, it is evident that any reduction in such difference by properly operating the chambers in sequence results in improvements in efficiency of the arrangement.
The chambers of the arrangement are all of equal lengths and, because of their substantial lengths, they may be bent once or several times in order not to take up an inordinate amount of space and to facilitate their operation and control.